How do we know whether screening for something like cervical cancer is effective at saving women's lives? Two ongoing studies conducted in India (one funded by the National Cancer Institute and the other by The Gates Foundation) are aimed at answering that question — but their methods are under fire by critics.

It works like this. Say you want to test the effectiveness of a new screening method. You recruit a large group of women and you split them into two groups. One group gets the screening regularly. The other, the control group, doesn't get the screening. Then you follow them over time and track how many women in both groups died of cancer. That's a pretty basic scientific method. It's also something that prompts big questions about the treatment of women in the control group.

The people conducting the study say women in the control group were told they could seek out screening on their own. Critics argue that point (and the way the study worked) wasn't clearly explained, and that those alterante options weren't as available to the women as researchers imply. The majority of the women participating in the studies are poor and have very little formal education.

There are some important differences between this and the infamous Tuskegee syphilis experiment. In that case, researchers identified men with syphilis and neither told them about their disease nor offered them treatment — just monitored the deadly disease's progress. Here, there's clearly an attempt (however poorly executed) at being open with the women about what the study is and what is being done. And nobody is intentionally trying to prevent sick women from being treated. But the study definitely exists in an uncomfortable space and could reasonably be called unethical. Is it ever okay to not screen people for a disease that are pretty sure some of them have? If not, how do we figure out whether potentially life-saving screening methods are actually useful? How do you do statistics ethically when people are the numbers? I don't have good answers for these questions.

Here's what we do know. There are 76,000 women enrolled in the National Cancer Institute study, and another 31,000 in The Gates Foundation study. So far, they've been tracked for 12 years and at least 79 of the women in the control groups have died of cervical cancer.